When there is a discrepancy with the stone vs records, I am pretty sure the policy is that they are supposed to use the date on the stone, but they can have an explanation in the biography portion, which many do, especially if a source is sent. I have seen my source link posted frequently when that occurs, sometimes even when the date matches and it was changed. We also have to remember that the 'age' and the 'birthdate' are being done by someone that was not there at the time of birth usually. Many people forgot what year they were born or had been using a false year for different reasons, also, so the sources are always the best to use, but not necessarily the Death source for the birth year.